fix ed25519 in yocto

Author: aidangarske

src/wp_ecx_exch.c

@@ -571,58 +571,33 @@ static int wp_x25519_derive(wp_EcxCtx* ctx, unsigned char* secret,
                 fflush(stderr);
             }
 
-            /* CRITICAL FIX: Force-clear MSB on BOTH keys right before calling shared_secret */
-            /* wc_curve25519_shared_secret checks MSB from internal key structure, not exported bytes */
-            /* Even if exported bytes show MSB clear, internal structure might have it set */
-            fprintf(stderr, "[X25519-DEBUG] wp_x25519_derive: [BEFORE] Force-clearing MSB on both keys before shared_secret call...\n");
-            fflush(stderr);
-            
-            if (ok && pre_call_local_rc == 0 && pre_call_peer_rc == 0) {
-                /* Force-clear MSB on LOCAL key's public key */
-                byte local_pub_fixed[CURVE25519_KEYSIZE];
-                XMEMCPY(local_pub_fixed, pre_call_local_pub, CURVE25519_KEYSIZE);
-                local_pub_fixed[CURVE25519_KEYSIZE - 1] &= 0x7f;
-                fprintf(stderr, "[X25519-DEBUG] wp_x25519_derive: [BEFORE] LOCAL key - before fix: 0x%02x, after fix: 0x%02x\n",
-                        pre_call_local_pub[CURVE25519_KEYSIZE - 1], local_pub_fixed[CURVE25519_KEYSIZE - 1]);
-                fflush(stderr);
-                /* Re-import LOCAL public key with MSB cleared */
-                int rc_local_fix = wc_curve25519_import_public_ex(local_pub_fixed, CURVE25519_KEYSIZE, local_key, EC25519_LITTLE_ENDIAN);
-                fprintf(stderr, "[X25519-DEBUG] wp_x25519_derive: [BEFORE] LOCAL key re-import with MSB cleared: rc=%d\n", rc_local_fix);
-                fflush(stderr);
-                
-                /* Force-clear MSB on PEER key's public key */
-                byte peer_pub_fixed[CURVE25519_KEYSIZE];
-                XMEMCPY(peer_pub_fixed, pre_call_peer_pub, CURVE25519_KEYSIZE);
-                peer_pub_fixed[CURVE25519_KEYSIZE - 1] &= 0x7f;
-                fprintf(stderr, "[X25519-DEBUG] wp_x25519_derive: [BEFORE] PEER key - before fix: 0x%02x, after fix: 0x%02x\n",
-                        pre_call_peer_pub[CURVE25519_KEYSIZE - 1], peer_pub_fixed[CURVE25519_KEYSIZE - 1]);
-                fflush(stderr);
-                /* Re-import PEER public key with MSB cleared */
-                int rc_peer_fix = wc_curve25519_import_public_ex(peer_pub_fixed, CURVE25519_KEYSIZE, peer_key_derive, EC25519_LITTLE_ENDIAN);
-                fprintf(stderr, "[X25519-DEBUG] wp_x25519_derive: [BEFORE] PEER key re-import with MSB cleared: rc=%d\n", rc_peer_fix);
-                fflush(stderr);
-                
-                if (rc_local_fix != 0 || rc_peer_fix != 0) {
-                    fprintf(stderr, "[X25519-DEBUG] wp_x25519_derive: [BEFORE] ERROR - Failed to re-import keys with MSB cleared! local_rc=%d, peer_rc=%d\n",
-                            rc_local_fix, rc_peer_fix);
+            /* NOTE: We do NOT normalize the local key here because:
+             * 1. The local key already has both public and private keys
+             * 2. Re-importing only the public key can corrupt the key structure
+             * 3. The local key was generated properly and should already have MSB clear
+             * 
+             * The peer key should already be normalized in wp_ecx_set_peer, but we check
+             * and normalize only if MSB is actually set (to avoid unnecessary operations).
+             */
+            if (ok && pre_call_peer_rc == 0) {
+                /* Only normalize peer key if MSB is actually set */
+                if (pre_call_peer_pub[CURVE25519_KEYSIZE - 1] & 0x80) {
+                    fprintf(stderr, "[X25519-DEBUG] wp_x25519_derive: [BEFORE] Peer key has MSB set, normalizing...\n");
                     fflush(stderr);
-                    ok = 0;
-                } else {
-                    /* Verify the fix worked */
-                    word32 verify_local_len = CURVE25519_KEYSIZE;
-                    word32 verify_peer_len = CURVE25519_KEYSIZE;
-                    byte verify_local[CURVE25519_KEYSIZE];
-                    byte verify_peer[CURVE25519_KEYSIZE];
-                    int verify_local_rc = wc_curve25519_export_public_ex(local_key, verify_local, &verify_local_len, EC25519_LITTLE_ENDIAN);
-                    int verify_peer_rc = wc_curve25519_export_public_ex(peer_key_derive, verify_peer, &verify_peer_len, EC25519_LITTLE_ENDIAN);
-                    if (verify_local_rc == 0 && verify_peer_rc == 0) {
-                        fprintf(stderr, "[X25519-DEBUG] wp_x25519_derive: [BEFORE] Verification after fix - LOCAL last_byte=0x%02x (MSB=%s), PEER last_byte=0x%02x (MSB=%s)\n",
-                                verify_local[CURVE25519_KEYSIZE - 1],
-                                (verify_local[CURVE25519_KEYSIZE - 1] & 0x80) ? "SET" : "CLEAR",
-                                verify_peer[CURVE25519_KEYSIZE - 1],
-                                (verify_peer[CURVE25519_KEYSIZE - 1] & 0x80) ? "SET" : "CLEAR");
+                    
+                    byte peer_pub_fixed[CURVE25519_KEYSIZE];
+                    XMEMCPY(peer_pub_fixed, pre_call_peer_pub, CURVE25519_KEYSIZE);
+                    peer_pub_fixed[CURVE25519_KEYSIZE - 1] &= 0x7f;
+                    
+                    int rc_peer_fix = wc_curve25519_import_public_ex(peer_pub_fixed, CURVE25519_KEYSIZE, peer_key_derive, EC25519_LITTLE_ENDIAN);
+                    if (rc_peer_fix != 0) {
+                        fprintf(stderr, "[X25519-DEBUG] wp_x25519_derive: [BEFORE] ERROR - Failed to normalize peer key! rc=%d\n", rc_peer_fix);
                         fflush(stderr);
+                        ok = 0;
                     }
+                } else {
+                    fprintf(stderr, "[X25519-DEBUG] wp_x25519_derive: [BEFORE] Peer key MSB already clear, no normalization needed\n");
+                    fflush(stderr);
                 }
             }